Australian hand-powered flight uses mulga wood which is one of the hardest timbers . Aboriginal mulga blade weapons are 2ft x 2inch x 1/2 inch. Maybe there are 2ft prop blades which are 1/2 inch thick but maybe generally not that thin. Perhaps a large model-plane prop could be 1/2".

This question is on the fringes of "propellors".

So if these thin props exist , are there any cases of injury to the skull by a prop with the type of bone-fracture known? One girl in Texas had a head wound but didn't reply to me . An ancient skull has been found with a sword-cut , explained as being by mulga blade , but I don't believe it . There's jail time for testing on a person . Any comments on what a prop does to skull?

Dr Michael Westaway
"When you look carefully at these sort of lesions, the striations are fairly diagnostic of an edged steel weapon. .. This is significant because we actually haven't seen anything like this in the archaeological record in Australia before. ...Nothing that we've seen with this man seems to sit comfortably with what has already been recorded by archaeologists.. .. Looking at the experiments on bone that have been published in the United States and elsewhere, we can see that edged weapons, and swords in particular, create traumas very similar to what we're seeing in the man from Toorale."
--------------------

"..Of the weapons tested, the frontal wound observed in Kaakutja most closely resembles that produced by an African ‘Samburu’ sword. .. only a traditional, Aboriginal, sharp-edged weapon could have inﬂicted the trauma. "

---------
A test on pig-skull using a mulga-wood blade failed:

" I have received the following comment from the writer ( an honours student): " The aim of the experiments were to determine whether traditional Aboriginal weapons could have caused trauma similar to that of the Toorale skull. Unfortunately our methods did not produce trauma,.. "

ANU College of Arts and Social Sciences. "
------
When I write to medical research about using wood for surgical chisels , they don't reply , which is waste of this breakthrough in bone bashing.

I did a research paper years ago looking at 280+ propeller injuries at the NTSB. The mechanism of injury, however is really different, as there is a lot of mass and a lot of momentum involved in aircraft propeller movement, and even at idle there is combustion force at play. In addition, aircraft propeller injuries often involve multiple blade impacts in a very short period of time.

This question may be better answered by a physicist, calculating mass, speed and force compared to compression strength of bone.

Thanks , bone marrow is about 40% water so the Resistance is Velocity sq. And at increased velocity above 150 ft/sec a 1/4 inch and 3/8 inch steel ball cause increasingly explosive damage . Maximum baseball pitching is around 100 mph , 150 ft/sec as is ice-hockey puck . Baseball bat and an ice-puck cause comminuted depressed fractures in skull . The blade of a heavier sword at 2ft would be at twice max arm speed and slices bone like butter or cream .

A mulga blade would have about 18Newtons and a large Indonesian kris sword about 24Newtons.

" For their test subject, the MythBusters crafted a dummy sporting a humanlike head stuffed with brainlike ballistics gel and pig skull.The weapon of choice was a standard household fan with 52-inch (132-centimeter) wooden blades that turned at a top speed of 26 miles per hour (42 kilometers per hour).

Neither jumping directly into the fan nor leaping toward the blades at an angle did much damage to the dummy. At worst, someone might suffer a concussion or a bloody nose, but the blades are too dull and slow to decapitate.

The industrial fan — complete with powerful motor and metal blades that whip around at 54 miles per hour (87 kilometers per hour) — did more damage. The blades acted like rotating machetes, slicing straight through the neck, jugular and vertebrae. However, since the dummy managed to escape with his head still attached, the original myth remained busted."

Thickness of blade seems to be significant. Swords are 1/12-1/8 inch and mulga blades are bi-convex , 1/4 - 1/2 inch thick at 1/2 inch back from edge. The cutting-tip angle is 60-90degrees , the Toorale skull was struck at about 45degrees and the rear jaw is sliced meaning the blade was turned to dig in . So a wood blade would be very blunt compared with sword.

The NTSB records don't include autopsy or medical records, so there's no way of knowing that information in detail.

I would suggest that using composition of bone of 40% water is a flawed premise to a theory of impact resistance of the skull. The skull contains some bone marrow but is largely cortical bone, which is very dense and very strong.